1. Technical Field
The present invention generally relates to automatic transmissions. More specifically, but without restriction to the particular embodiment and/or use which is shown and described for purposes of illustration, the present invention relates to an automatic transmission having a primary and alternate speed ratio within the same gear.
2. Discussion
Automotive drivetrains generally include similar basic components. An internal combustion engine, or some other type of power plant, is typically the primary source of power on board a vehicle. An internal combustion engine produces power by converting chemical energy from a liquid fuel into mechanical energy of motion. The engine produces power that ultimately will drive the wheels of the vehicle. The major drivetrain component between the wheels and the engine is a transmission. The transmission translates engine torque to the wheels. The primary function of an automotive transmission is to provide the proper speed ratio between the rotational speed of the engine and the desired rotational speed of the wheels. The transmission also controls the direction of rotation applied to the wheels so that the vehicle may be driven forward and backward.
Transmissions are typically automatic, manual or some combination thereof. Automatic transmissions are designed to take automatic control of the frictional units or clutch elements, speed ratio selection and gear shifting. A thorough description of general automatic transmission design principals may be found in "Fundamentals of Automatic Transmissions and Transaxles," Chrysler Corporation Training Manual No. TM-508A, which is incorporated herein by reference. Additional descriptions of automatic transmissions may be found in U.S. Pat. No. 3,631,744, entitled "Hydromatic Transmission," issued Jan. 4, 1972 to Blomquist, et al., U.S. Pat. No. 4,951,200, entitled "Method of Controlling the Apply Element During A Kick-Down Shift For An Electronic Automatic Transmission System", issued on Aug. 21, 1990 to Leising, et al., U.S. Pat. No. 4,289,048, entitled "Lock-up System for Torque Converter," issued on Sep.15, 1981 to Mikel, et al., and U.S. Pat. No. 4,875,391, entitled "Electronically-Controlled, Adaptive Automatic Transmission System" issued on Oct. 24, 1989 to Leising, et al. The aforementioned patents are owned by the assignee of the present application and are incorporated herein by reference.
Generally, automatic transmissions include gear elements for defining several different forward speed or gear ratios between the input and the output shaft of the transmission, the input shaft being linked to the engine and the output shaft being indirectly linked to the wheels. The shifting between speed ratios is facilitated by a number of clutches that can be applied and released by hydraulic pressure to create an array of speed ratios between the input and output shaft. Typically, two clutches are applied to create a forward speed ratio. When a change from one speed ratio to another is desired, one of the applied clutches releases as another clutch applies to create a speed ratio different from the previous speed ratio. The clutches are attached to various gear sets, when certain clutches are applied torque is delivered to the proper gear sets to produce the desired ratio.
A transmission has a number of gears, typically, first, second, third and fourth gears. Typically, each gear has an associated speed ratio. The speed ratio created by the application of fluid operated clutches is typically defined as Ni/No, where Ni is the input shaft speed and No is the output shaft speed. The lower the gear, the higher the speed ratio. Conversely, the higher the gear, the lower the speed ratio. Accordingly, a shift from a given speed ratio to a lower speed ratio is termed up-shifting, while a shift from a given speed ratio to a higher speed ratio is termed downshifting. Typically, an automatic transmission only up-shifts to adjacent gears while downshifting may occur to non-adjacent gears to accommodate certain driving situations.
The art of shifting a transmission has been grounds to many innovations over the years. The precise speed ratios utilized as well as the shifting sequence is crucial in developing a drivetrain that is smooth and efficient. There is a continual need to develop drivetrains that are more efficient, shift more smoothly, minimize engine noise, and increase performance. Developing unique shifting schemes as well unique speed ratio configurations can help in meeting this continual need for drivetrain development.